The present invention generally relates to hydrogen storage systems and methods. More particularly, this invention relates to a system and method for recharging a porous hydrogen storage media through the use of a catalyst, and by which up to almost 100% of the original quantity of hydrogen stored in the media can be replenished.
Hydrogen fuel cells are being considered for a wide variety of power applications, including but not limited to mobile applications such as vehicles. However, more conventional hydrogen storage technologies suffer from significant drawbacks that make them ill-suited for mobile applications such as passenger vehicles. For example, compressed hydrogen gas requires heavy tanks and very high pressures that would pose a potential hazard in a crash, and liquified hydrogen can cause skin damage if released and requires active refrigeration that is energy-intensive and requires considerable insulation. Hydrogen storage for vehicles and other mobile applications would benefit from solid-state storage, which uses more moderate temperatures and pressures, and is thus more attractive for use with vehicles as well as other applications, including stationary power systems and consumer electronics.
The use of porous silicon as a solid-state storage media for hydrogen is quite new, as exemplified by U.S. Published Patent Application No. 2004/0241507 by Schubert et al. and a paper authored by Lysenko et. al., in J. Phys. Chem. B 2005, 109, pg 19711-19718. Both focus on the initial charge of hydrogen in a porous silicon media, with little emphasis concerning recharging the media. In Schubert, et al., the description briefly mentions the use of catalysts, teaching that chemical activation may include the electrodeposition of a catalyst, for example, palladium or platinum, onto a silicon surface to facilitate bonding of hydrogen to the surface. Schubert et al. also teach that the activation energy of silicon can be enhanced, such as by deposition of a catalyst material to reduce the energies of adsorption or desorption from a silicon surface. As such, Schubert et al. are concerned with modifying the bond energy of hydrogen to a silicon surface for purposes of attaching or detaching hydrogen.
A complication with the use of silicon as a hydrogen storage media is the tendency for silicon to reform upon dehydrogenation. In other words, once hydrogen atoms leave the silicon atoms to which they are bonded, the remaining silicon dangling bonds reconnect with their neighbors through silicon-to-silicon bonding, making a substantial fraction of the original bond sites no longer available to participate in hydrogen storage. Farjas et al., Phys. Rev. B, 65, (2002) 115403, entitled “Calorimetry of Hydrogen Desorption from a-Si Nanoparticles,” experimentally verified that 96% to 99% of dangling bonds recombine upon dehydrogenation of amorphous silicon films. Such low recharge capabilities render gaseous recharging of solid-state hydrogen storage systems impractical for vehicular and many other applications, and consequently necessitates recharging by aqueous methods. While aqueous recharging methods are known and practical, gaseous recharging methods have certain advantages, including initial acceptance and planning by industry and government agencies.